Many orthopedic surgery procedures, particularly spinal surgery procedures, require surgeons to drive multiple screws into a patient's spine. During such delicate procedures, it is important for the surgeon to have a high degree of control and tactile feedback from any instrument used to drive the screws. This is important so that the necessary torque is applied to the screwdriver without overtightening the screws, which can damage the bone or the surrounding tissue and lead to injury or damage to the spinal cord. Moreover, control and feedback are useful to ensure that the screw is advanced properly into the bone, which includes maintaining the screw along the proper axial alignment.
Additionally, as in most surgeries, it is advantageous in spinal surgery that the procedure is performed as quickly as possible. Therefore, it is desirable to be able to advance the screws into the spine quickly. Automatic screwdrivers, including those which are driven by an electric motor or the like, are known for quickly driving screws. However, such devices do not provide much tactile feedback or control. Hand-driven screwdrivers are therefore preferred, despite lacking the speed advantage provided by automatic screwdrivers.
The design of screw threads has been altered as one possible solution to the problem of increasing the speed with which screws are advanced into bone, particularly during spinal surgery. For example, screws have been developed that include multiple, most frequently two, start threads. This arrangement allows for the threads to be positioned at a higher pitch, while maintaining the overall number of threads. The steeper pitch increases the speed at which the screw can be inserted into the bone by reducing the number of revolutions required in order to advance the screw by a given length. However, the steeper pitch of the threads may increase the likelihood of screw backout, which can be damaging to the tissue surrounding the spine and may lead to the instability of anything held in place by the screws.
It is therefore desired to provide an arrangement that provides the control and tactile feedback of a hand-driven screwdriver, while increasing the speed at which screws can be driven. Such a device should provide these advantages while being compatible with various types of screws, including those that have a single start thread.